Istanbul: Fresh violence erupted in Turkey as protesters defied a government plea to end days of deadly unrest, which is said to have posed the biggest challenge yet to Prime Minister Recep Tayyip Erdogan's decade-long rule.

The police used tear gas and water cannon on hundreds of protesters who ignored warnings to disperse in Istanbul, Ankara and the southeastern city of Hatay, where a young protester died a day earlier.

"You are being unfair to us, that is enough!" one protester was seen yelling at the police after warnings were issued to quit an area close to Erdogan's Istanbul office.

Erdogan's government had earlier won praise from the United States for apologizing to injured protesters, but that concession did not appear to have stemmed popular anger.

Thousands gathered at Istanbul's Taksim Square, with protests entering its sixth day, yelling defiance at Erdogan, who earlier has dismissed the protesters as "extremists" and "vandals". He was in Algeria on the second day of a four-day official visit to north Africa.

"The vandals are here! Where is Tayyip?" yelled the crowd.

They accuse Erdogan, who has won three successive national elections, of imposing conservative Islamic reforms on the predominantly Muslim but constitutionally secular nation.

"If they step back, if they change something in Turkey, the conservatism and the things they've done, then maybe the crowd can go home," said Didem Kul, a 24-year-old student in Taksim Square.

Turkish pipe music and singing blared over speakers as the crowd clapped along. The festive atmosphere was in stark contrast to the tense rallies of the past five days.

Even fans from rival football teams Galatasaray, Besiktas and Fenerbahce linked arms, united in protest.

Earlier on Wednesday, Deputy Prime Minister Bulent Arinc apologized to protesters who sustained injuries when the clashes erupted last week. The wave of protests broke out on Friday last week after police released tear gas on demonstrators at a peaceful rally against plans to build on an Istanbul park.

"I apologize to those who were subjected to violence because of their sensitivity for the environment," he said, though he added that his apology excluded "the rioters.”

"The government has learnt its lesson from what happened," he added. "We do not have the right and cannot afford to ignore people. Democracies cannot exist without opposition."

Two people have been killed in the clashes, officials and medics say, and rights groups say thousands have been injured. The government puts the figure at around 300.

Erdogan, whose Justice and Development Party (AKP) first took power in 2002, has accused the main opposition Republican People's Party of having a hand in the protests.